The present invention relates to plastic molding. More particularly, the invention relates plastic molding in two different colors, and a method of manufacturing such plastic molding. The method utilizes a mold which facilitates formation of various symbols.
Plastic moldings made to have two colors are widely used to prepare, for example, key tops of an input means like a keyboard or typewriter, the colored part forming letters and signals which function to permit visual selection or inspection of input and output information. A key top of the prior art is made of plastic material, hereinafter called the first part molding, which indicates the sign O in a certain color such as, for example, gray, such as N8 of the Munsell color system. Plastic material, hereinafter called the second part molding, is placed against the first part molding and forms the part encircled by the sign O and the part outside such sign. The second part molding is a color other then gray such as, for example, dark gray, such as 5B3/0.5 of the Munsell color system.
Heretofore, the aforedescribed key top has been made generally by steps utilizing an outer die and an inner die for making the first part molding. The outer and inner dies are positioned facing each other at a predetermined place to form a cavity into which soft gray plastic material is injected to form the first part molding. The outer die of the first part molding is then removed, and a pin which movably extends through the inner die is slightly lowered to form a tunnel shape path beneath the part of the first part molding making the sign O. An outer die the second part molding is then positioned at a predetermined place to face the inner die in a manner whereby it covers the first part molding. At such time, soft dark gray plastic material is injected into a cavity formed by the outer die to prepare the second part molding. The key top is thus completed.
Manufacture of the aforementioned moldings is carried out by an injection molding machine having a first cylinder 21, a first cavity plate 22, a first strip plate 23, a first core 24, a slide core plate 26, a cam 27 and an eject plate 28. The machine also has second identical parts. The core carrying part of the known apparatus rotates and moves vertically.
A pin is required for making moldings that have letters with enclosed areas such as, for example, capital letter signals A, B, D, and the like. The pin must be provided in the enclosed area. Then, soft plastic material for the second part molding is injected into the enclosed area. Because of this, there have been problems that, for each outer die for the first part molding used to make various patterns of signs having the enclosed area, an inner die corresponding to the outer die had to be prepared.
The principal object of the invention is to provide a plastic molding and method which overcome the problems experienced in the prior art.
An object of the invention is to provide a plastic molding and method which considerably reduce the cost of preparing dies.
Another object of the invention is to provide a plastic molding and method which dispense with the means for replacing the inner die.
Still another object of the invention is to provide a plastic molding and method which are of greater precision than heretofore.
Yet another object of the invention is to provide a plastic molding and method which increase the manufacturing yield of two color moldings.